The nature of the long haul trucking industry and certain governmental regulations impact professional truck drivers' lives in significant ways. A driver's rest or sleep time is one aspect of his/her life that is impacted.
A highway truck may be equipped with a sleeper cab that enables a driver to park a rig and then rest or sleep, or to allow one of a pair of companion drivers to do so while the other drives. To address personal needs of the driver and any companion, the cab may be equipped with various electrical accessories that provide useful conveniences during long haul runs. A driver and/or companion may also have their own personal accessories that are electrically operated and may run on household electricity, rather than on the DC battery bank voltage that is typically available in trucks.
In order to accommodate such personal accessories, and other on-board equipment that may also run on AC household electricity, a long haul truck may have either some type of device such as an inverter for converting DC battery bank voltage into 115 volt, 60 hertz, AC electricity, or an APU (auxiliary power unit) that generates 115 volt, 60 hertz, electricity. If a truck has neither, it may instead have to rely on connecting to an off-board power grid when stationary at a location such as a truck stop that has such a grid. If a truck stop where the truck stops has no such grid, the driver and/or companion cannot use electric AC devices or appliances in the truck.
If an on-board inverter is operating to supply AC power while the truck is being driven, the battery bank can be kept charged by an engine-driven charging system. If the inverter is operating to supply electricity while the truck is stationary, battery bank charge will be drawn down unless the engine is idling to keep the charging system operating.
An APU typically operates at times when the engine that propels the truck is shut off. Electrical loads that use AC electricity from the APU therefore do not deplete battery bank charge. Because most highway trucks are propelled by engines that use diesel fuel, the engine of a typical APU is a diesel engine that draws diesel fuel from the existing fuel tanks in the truck.
An APU diesel engine may power an electric generator that develops typical household AC voltage at regulated 115 VAC, 60 hertz. Electrical devices and accessories, many of which would be considered common household accessories, can be plugged into receptacles in a truck sleeper compartment that are connected to the regulated AC voltage. The regulated AC voltage can also be used to maintain the truck's battery bank charge as needed while the engine in the powertrain that propels the truck is not running.
Various APU models are commercially available from different manufacturers. However, certain trucks that have sleeper cabs may not have an on-board source of regulated AC voltage, such as an APU or an inverter. Even if such a truck lacking an APU were to have an inverter, the inverter might be unable to supply all the demands of in-cab conveniences that run on household electricity.
Those demands may only be met when the truck is stationary at a location such as at a truck stop where the truck's electrical system can be plugged into a receptacle that supplies household AC electricity. Such a source of electricity is sometimes referred to as “shore power”, and such a truck is said to be capable of accepting “shore power”.